The design of inlet size for hydrocyclone is an effective method to improve separation accuracy. However

for a long term

the study on hydrocylone inlet size is largely dependent on practical experience. Few studies have been on the influence of inlet size on the hydrocyclone flow field. In this article

the flow field inside a 50 mm hydrocyclone is investigated with CFD method. The pressure profile

three-component velocity distribution and secondary vortex structure are analyzed. The results show that the tangential velocity is the component being affected most since it grows apparently

while the axial and radial velocities vary less

which means that the centrifugal factor increases while the separation structure keeps similar. The swirl velocity of the flow in the far side from the inlet is reinforced. The double-peak phenomenon is found in axial velocity and the reduction of inlet size magnifies this effect. In this sense

the flow field with smaller inlet is prone to better separation. However

smaller inlet size facilitates the formation of secondary vortexes and enhances the entrainment of fluid by the injected flow

which may hamper the separation. Thus

the cut-off size will not always decrease with the reduction of inlet size. Moreover

the increase of energy consumption is mostly attributed to the greater local loss in the connection of inlet and cylinder and the formation of more secondary vortexes.